Build Your First Performance Engine - Part 3: Cylinder Head Prep

JGM machined a 45-degree seat on the existing valves and added a 30-degree back-cut to both the intake and exhaust valves. One mark of a good valve job is the seat being positioned as far to the outside edge of the valve as possible.

JGM machined a 45-degree seat on the existing valves and added a 30-degree back-cut to bot

Flow Testing
Since these were older heads, we noticed the valves were not back-cut. To test the effect of the back-cut, we flow-tested the heads first in their original, used condition, then after a valve job, and finally with the additional 30-degree angle. On the exhaust side, the results were well worth the effort; on the intake side, you could make a case to either use it or not.

Flow Chart
Test 1: This is the flow with the used heads right off the engine.
Test 2: Same heads and valves with a JGM valve job.
Test 3: Added a 30-degree back-cut to both intake and exhaust.

All tests were performed on a SuperFlow 600 flow bench at 28 inches of test depression using both SuperFlow's FlowCom digital data and Performance Trends' Port Flow Analyzer computer program.

We were interested in how much a 30-degree back-cut might be worth on these AFR heads. The exhaust benefited as much as 15 cfm, but on the intake side, it was a wash.

We were interested in how much a 30-degree back-cut might be worth on these AFR heads. The

Iron versus Aluminum
There's also the question of purchasing used high-performance iron heads versus used aluminum heads. We can honestly say that regardless of the flak you've read on the Internet, there is no difference in power assuming the heads flow the same. The beauty of aluminum is that even when there's a crack or a munched combustion chamber, it's very easy to repair. These same difficulties with an iron head require much more money, time, and hassle to repair. Now that most companies mainly offer heads in iron to fit into some budget race class, the smart move is to save the weight, spend a little more in the beginning, and use an aluminum head. If nothing else, when it comes to dropping heads on a big-block FE Ford, you won't need an engine hoist if you go with a set of aluminum heads.

Used versus New
In many cases, the ultimate choice of high-performance cylinder heads comes down to a question of money. Many enthusiasts believe it's cheaper to rebuild a set of existing iron castings than it is to invest in a new set of heads. This is usually based on obtaining the basic castings for a budget price. Unfortunately, this approach often results in investing good money in a weak set of production-based heads.

The following price chart lists the generally accepted steps necessary to rebuild a set of used cylinder heads. These prices came from Jim Grubbs Motorsports and may not be reflective of pricing structures across the country, but unless you can get this work done at half the cost, you're still looking at investing $600 to $900 in a set of heads, and that does not include the cost of new valves, springs, retainers, keepers, studs, or valve-stem seals. For a small-block Chevy, you can purchase a brand-new set of TFS 195cc heads that will make more torque and horsepower than any factory Gen I head for only slightly more money.

Of course, there is a major case for rebuilding a set of used performance aluminum heads. In our case, the AFR 210s turned out to be in great shape, requiring only a mild cleanup and a valve job, but not all used heads turn out to be a good choice. Above all, avoid ported heads unless you either know the heads' complete history or have access to a flow bench where you can evaluate the quality of the work. Most backyard porting jobs end up hurting the flow more than helping. And also remember that if the deal seems to good to be true, it probably is.